Method and system for solventless calibration of volatile or semi-volatile compounds

ABSTRACT

A system for solventless calibration of volatile or semi-volatile compounds and methods thereof. The system includes a fluid path having a first end configured to be operably coupled to a fluid source and a second end configured to be operably coupled to the analytical instrument. A solid sorbent is disposed along the fluid path and is configured to absorb an analyte. The flow of fluid along the fluid path from the first end to the second end causes absorbed analyte to be desorbed from the solid sorbent at a desired concentration to the instrument.

This application is a continuation of U.S. application Ser. No.16/283,977 (pending), filed Feb. 25, 2019, which claims the benefit ofand priority to prior filed co-pending Provisional Application Ser. No.62/634,351, filed Feb. 23, 2018. The disclosure of each of theseapplications is incorporated herein by reference in its entirety.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

FIELD OF THE INVENTION

The present invention is related to improved analytical techniquesuseful for the identification and enhanced quantification of chemicalspecies, such as chemical warfare agents.

BACKGROUND OF THE INVENTION

Analytical chemistry is the science of obtaining, processing, andderiving information about a composition of matter. Variousinstrumentation modalities exist to facilitate obtaining theinformation, whether qualitative or quantitative, and include, forexample, chromatographs, spectrometers, electrochemical cells,microscopy, and so forth.

Before an analytical instrument can return beneficial information, theinstrument often requires calibration. Calibration is the comparison ofmeasured values to known values (or standards) and is necessary toobtaining both accurate and precise results. Generally, in analyticalchemical applications, a series of standards (known composition, calledan analyte, at known concentrations) are evaluated using the analyticalinstrument to derive a standard curve. Samples of unknown composition orquantity may then be evaluated against the standard curve.

However, there are some difficulties associated with calibrations,particularly when an analysis is performed outside a conventionallaboratory setting (e.g., a remote area or a moving vehicle, oftenreferenced as “in the field”). Analysis in the field may be complicatedor rendered impossible by little-to-no access to necessary standards.Some standards, such as those associated with volatile or semi-volatileanalytes, (organic compounds, such as poly-aromatic hydrocarbons,pesticides, nitrosamines, and organo-phosphates) are particularlychallenging because analysis requires these analytes to be infused intodevices without the addition of solvents. Yet, conventional analyticalinstrumentation all require solvents to administer the standards.

Another complicating factor in the field is contamination. Not only mustthe standards be available, but the quantity of standard must be knownbefore a useful calibration curve may be derived.

Thus, there remains a need for solventless calibration methods andstandards that may be used to overcome difficulties associated withanalytical work in the field.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing problems and othershortcomings, drawbacks, and challenges of conventional methods ofanalyzing chemical species in non-conventional, non-laboratory settings.While the invention will be described in connection with certainembodiments, it will be understood that the invention is not limited tothese embodiments. To the contrary, this invention includes allalternatives, modifications, and equivalents as may be included withinthe spirit and scope of the present invention.

According to one embodiment of the present invention, a system forsolventless calibration of volatile or semi-volatile compounds includesa fluid path having a first end configured to be operably coupled to afluid source and a second end configured to be operably coupled to theanalytical instrument. A solid sorbent is disposed along the fluid pathand is configured to absorb an analyte. The flow of fluid along thefluid path from the first end to the second end causes absorbed analyteto be desorbed from the solid sorbent at a desired concentration to theinstrument.

According to another embodiment of the present invention amicrocalibrator for solventless calibration of an analytical instrumentincludes a fluid path having a first end configured to be operablycoupled to a fluid source and a second end configured to be operablycoupled to the analytical instrument. First and second solid sorbentsare disposed along the fluid path. The first solid sorbent is configuredto absorb an analyte at a first concentration; the second solid sorbentis configured to absorb the analyte at a second concentration. The flowof fluid along the fluid path from the first end to the second endcauses absorbed analyte to be desorbed from the first solid sorbent, thesecond solid sorbent, or both.

Still another embodiment of the present invention includes amicrocalibrator for solventless calibration of an analytical instrumenthaving a fluid path having a first end configured to be operably coupledto a fluid source and a second end configured to be operably coupled tothe analytical instrument. First and second solid sorbents are disposedalong the fluid path. The first solid sorbent is configured to absorb afirst analyte; the second solid sorbent is configured to absorb a secondanalyte. The flow of fluid along the fluid path from the first end tothe second end causes the first absorbed analyte, the second absorbedanalyte, or both to be desorbed from the first solid sorbent or thesecond solid sorbent, respectively.

Disclosed is a device for solventless calibration utilizing a removableanalyte source and a pre-concentrator with a solid sorbent. The deviceis configured to then vaporize absorbed analyte from the solid sorbentand to direct the vaporized analyte to an analytical instrument, such asa spectrometer. The micro-concentrator may include a MEMS-based microhotplate having a discrete amount of solid sorbent on the hotplate. Thedevice may include various valves and filters for controlling flowthrough the device and reducing the risk of contamination of theanalyte. The device may include a T-junction for adding additional airto the fluid stream after the micro-concentrator. The device may includea controller for fixing the amount of time that fluid source flows alongthe fluid path, a data port operably connected to a controller, a buttonfor causing the analyte to exit the device, or combinations thereof.

The device may also utilize multiple micro-concentrators operating inparallel. In such instances, the device may allow eachmicro-concentrator to absorb analyte from the removable analyte sourceat a respective fixed concentration.

The device may also control a split valve along the fluid path after themicro-concentrator to allow a variable concentration of the analyte topass to the analytical instrument.

Yet another embodiment of the present invention is directed to a methodfor solventless calibration by loading a solid sorbent with an analyteand then initiating a fluid flow through the solid sorbent such thatanalyte desorbs from the solid sorbent. The fluid flow with the desorbedanalyte is directed to an analytical instrument.

Additional objects, advantages, and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description of the embodiments givenbelow, serve to explain the principles of the present invention.

FIG. 1 is a diagrammatic view of a solventless calibration systemaccording to an embodiment of the present invention.

FIG. 2 is a diagrammatic view of an embodiment of a pre-concentratorwith an exemplary analyte source.

FIG. 3 is a diagrammatic view of another embodiment of apre-concentrator.

FIG. 4 is a flowchart describing a method of using a solventless systemaccording to an embodiment of the present invention.

FIG. 5 is a diagrammatic view of another solventless calibration systemaccording to another embodiment of the present invention.

FIG. 6 is a diagrammatic view of a solventless calibration systemaccording to yet another embodiment of the present invention.

FIG. 7 is a graphical representation of a calibration curve obtainedusing a convention injection method.

FIGS. 7-10 are chromatographs resulting from the replications of low,medium, and high concentration of analyte using the calibration curve ofFIG. 6.

FIG. 11 is a graphical representation of a calibration curve obtainedusing a solventless calibration system according to an embodiment of thepresent invention.

FIGS. 12 and 13 are graphical representations of calibration curves ofthermal desorption tubes acquired by direct injection and by using asolventless calibration system according to an embodiment of the presentinvention.

FIGS. 14 and 15 are chromatographs illustrating changes associated withanalyte source replacement.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the sequence of operations as disclosedherein, including, for example, specific dimensions, orientations,locations, and shapes of various illustrated components, will bedetermined in part by the particular intended application and useenvironment. Certain features of the illustrated embodiments have beenenlarged or distorted relative to others to facilitate visualization andclear understanding. In particular, thin features may be thickened, forexample, for clarity or illustration.

DETAILED DESCRIPTION OF THE INVENTION

The disclosed invention is drawn to a device and method for solventlesscalibration, and specifically to a device and method that use a solidsorbent to absorb analyte from a removable analyte source, some or allof which is later vaporized and provided to an instrument, such as aspectrometer.

Referring now to the figures, and in particular to FIG. 1, amicrocalibrator 10 according to one an embodiment of the presentinvention is shown and includes a housing 12 and a fluid path 14extending through the housing 12. The housing 12 may be constructed froma durable material to protect sensors, electronics, and other componentswithin the housing 12. The housing 12 may also provide insulation fromexternal conditions. In some embodiments, the housing 12 may be sealedsuch that the components therein are waterproof or water resistant. Thehousing 12 may also include space or connections for a power supply,removable battery, fuel cell, or other power source components therein.

A first end 16 of the fluid path 14 is configured to be operably coupledto a fluid source 18; a second end 20 of the fluid path 14 is configuredto be operably coupled to an instrument 22. Exemplary fluids of thefluid source 18 may be air or an inert gas (such as CO₂ or O₂), or anyother fluid that may be used to transport an analyte of interest. Theinstrument 22 may be, for example, a gas chromatograph (“GC”), a GC-MassSpectrometer (“GC-MS”), or other known instrumentation. In one example,an Agilent 6890 with a split/splitless inlet and a nitrogen-phosphorusdetector (“NPD”) may be utilized.

Referring now to both FIGS. 1 and 2, the microcalibrator 10 furtherincludes a micro-concentrator 24 within the housing 12 and in fluidcommunication with the fluid path 14. The micro-concentrator 24 mayinclude a housing 26 having an inlet port 28 configured to receive fluidfrom the fluid path 14, an outlet port 30 configured to eject fluid intothe fluid path 14, and a hub 32 that is configured to receive an analytesource 34. While the illustrated embodiment should not be considered tobe limiting, the analyte source 34 may comprise a container 36 having acap 38 with pierceable septum 40 such that a needle 42 operably coupledto the hub 32 may pierce the cap 38 and permit analyte to move from thecontainer 36 and into the housing 26 of the micro-concentrator 24.However, other analyte storage devices and mechanism are known and maybe implemented as needed.

The micro-concentrator 24 further comprises a solid sorbent 44positioned within the housing 26. The solid sorbent 44 is configured toabsorb analyte. For example, when the septum 40 of the analyte source 34is pierced, analyte may flow into the housing 26 of themicro-concentrator 24 and be absorbed into the solid sorbent 44. As isknown in the art, porosity and selectivity of a solid sorbent may betailored. Exemplary solid sorbent compositions may include graphitizedcarbon black (“GCB”), activated carbon, porous polymers (such as2,6-diphenyl-p-phenylene oxide), or a xerogel (such as SiO₂). Methodsfor synthesizing and tailoring solid sorbent compositions are known, forexample, such as in U.S. Pat. No. 5,858,457, entitled PROCESS TO FORMMESOSTRUCTURED FILMS, incorporated by reference herein in its entirety.Other solid sorbent compositions may include commercially-availablematerials, such TENAX, HAYESEP, CHROMASORB, for example.

Still referring to FIGS. 1 and 2, an amount of analyte absorbed into themicro-concentrator 24 depends on an amount of solid sorbent 44 thereinas well as the tailored character of the solid sorbent composition.According to some embodiments, such as the one illustrated in FIG. 2,the solid sorbent 44 may be supported by or otherwise attached to aplate 46 (illustrated with an adhesive 48 attaching the solid sorbent 44to the plate 46); however, it would be understood by those of ordinaryskill in the art having the benefit of the disclosure made herein thatthe plate 46 may not be required in all embodiments. If fact, accordingto some embodiments, the solid sorbent 44 may be coupled to any internalwall of the housing 26 of the micro-concentrator 24 or otherwisesuspended within a volume of the housing 26.

The plate 46 may comprise a thin, silicon nitride (SiN) substrate havinga patterned metal heating element (not shown) deposited thereon.Alternatively, the plate 46 may comprise a substrate operable as aresistive heater. Regardless of the particular structure of the plate46, the plate 46 should be configured to be heated or otherwise provideheat to the solid sorbent 44 such that upon heating, analyte thermallydesorbs from the solid sorbent 44. Heating of the plate 46 may include,for example, the application of a small amount of current to thepatterned metal heating elements.

In yet other embodiments, the solid sorbent and plate may comprise aunitary structure. For example, FIG. 3 illustrates a micro-concentrator50 having a housing 52 with an inlet 54, an outlet 56, and a hub 58. Aplate 60 within the housing may comprise a SiN substrate that is coatedwith a solid sorbent composition, such as a template, porous xerogel. Asa result, the solid sorbent 62 surrounds, covers, or otherwise enclosesthe plate 60. According to this illustrated and related embodiments, theplate 60 may be dip-, spray-, or spun-coated with the solid sorbent 62.According to other embodiments, the solid sorbent 62 may be synthesizeddirectly onto the plate 60. For example, precursor sols for coating theplate 60 may be prepared by the addition of a cationic surfactant (CTABCH₃(CH₂)₁₅N(CH₃)₃Br) to a silica sol in a two-step acid-catalyzedprocess. In a first step, a solution of TEOS (Si(OC₂H₅)₄), ethanol,water, and HCl at mole ratios 1:3.8:1:5×10 may be refluxed at 60° C. Ina second step, performed at room temperature, water may be added and[HCl] increased to about 0.01 M, which corresponds to the minimumaverage siloxane condensation rate. After stirring for 15 min at 25° C.,the sols may be aged at 50° C. for up to 8 hrs and diluted with 2equivalents of ethanol. CTAB may then be added, in varying quantities,corresponding to concentrations, c_(o), ranging from 0.03 M to 0.11 M (1wt % to 5 wt %). The final reactant mole ratios TEOS:EtOH:H₂O:HCl:CTABwere 1:22:5:0.004:0.093-0.31.

Referring now again to FIGS. 1 and 2, and optionally according to someembodiments, the micro-concentrator 24 may include an RFID reader 64that is configured to read an RFID chip 66 of the analyte source 34 suchthat information about the particular analyte source 34 may be recordedor read by the micro-concentrator 24. Information transmitted mayinclude, for example, type of analyte being used, a lot numberassociated with analyte synthesis or containment, time at which theanalyte source 34 is attached to the micro-concentrator 24, a number ofinjections, and other information that may be useful for validation andquality assurance purposes. Those of ordinary skill in the art wouldreadily appreciate that alternative devices may also be used. Forexample, QR code, bar codes, and other such mechanisms may be used inlieu of the RFID reader 64 and chip 66. Moreover, it would be understoodthat the RFID reader 64 need not be coupled to the micro-concentrator24, but instead the reader 64 could be incorporated into a controller 68or other structural component of the microcalibrator 10.

In some embodiments, signals received via a data port may signal to thecontroller 68 that the instrument 22 is operably coupled to themicrocalibrator 10, the data port may receive control signals, data, orinformation from the instrument 22, a computer, or other source, orboth. Control signals may indicate sample size desired, timing for whenthe analyte is required, the concentration of analyte required, etc. Insome embodiments, the controller 68 may be programmed to makecalculations related to these inputs (such as receiving a request for acertain concentration of an analyte and determining operation of pumps,valves, etc.). In other embodiments, control signals may be used tooperate the controller 68 according to particular operating parameters,and the controller 68 implements the provided instructions.

Still referring to FIGS. 1 and 2 along with FIG. 4, a method 70 of usingthe microcalibrator 10 according to an embodiment of the presentinvention is described. At start, analyte may be loaded into themicro-concentrator 24 (Block 72). According to the illustratedembodiment, analyte may be loaded by coupling the analyte source 34 tothe micro-concentrator 24, at the hub 32, so that analyte may flow intothe micro-concentrator 24 and absorb onto the solid sorbent 44. Asdescribed in detail above, an amount of analyte absorbed by the solidsorbent 44 depends on a volume of the solid sorbent 44 and theparticularly tailored character of the solid sorbent composition.

With the solid sorbent 44 wetted (the sorbent 44 may be fully wetted tosaturation but it is not required), flow from the fluid source 18 andinto the microcalibrator 10 may be initiated (Block 74). In this regard,and according to the illustrated embodiment, the controller 68 may beconfigured to open one or more valves 76, 77, 81, operate a pump 78, orcombinations thereof to permit fluid flow from the fluid source 18 tothe micro-concentrator 24. However, it would be understood that theoperation of valves, pumps, and the like would depend on the particularembodiment of the microcalibrator used.

While a flow rate of the fluid may be varied according to a particularneed or preference, in some embodiments the flow rate through themicro-concentrator may be less than about 500 mL/min. In otherembodiments, the flow rate may range from about 5 mL/min to about 100mL/min; and in still other embodiments, the flow rate may range from itis between about 5 mL/min and about 20 mL/min.

Optionally, and as would be understood by those of ordinary skill in theart, a gas trap 80 with associated valve 81 may be incorporated betweenthe fluid source 18 and the micro-concentrator 24 as a source of air tothe fluid path 14. The gas trap 80 may draw in purified air along aseparate line 83 or, otherwise, the line 83, the gas trap 80, or bothmay include a filter for purification and removal of contaminants duringair flow. For example, the trap 80 may be used to remove hydrocarbons,moisture, oxygen, or other elements in order to reduce the risks ofcolumn damage, loss of instrument sensitivity, or instrument downtime.In those embodiments in which the fluid is ambient air, the trap 80 maybe used to remove the analyte of interest such that the only analytepermitted into the micro-concentrator 24 is from the analyte source 34.

Analyte may then be desorbed from the solid sorbent 44 and vaporized formovement to the instrument 22 (Block 82). While the manner by which theanalyte desorbs is dependent on the particular solid sorbentcomposition, in the illustrated embodiment of FIG. 2, fluid flow,resistive heating, or both may be used to release the analyte from thesolid sorbent 44. As noted above, desorption may include the control ofthe valves 76, 77, 81, the pump 78, resistive heaters (not shown) orother structural elements that depend on the particular embodiment.

With the analyte vaporized, the analyte may be directed to theinstrument 22 for measurement of the control (Block 84), which mayinclude the control of the valves 76, 77, 81, the pump 78, orcombinations thereof. According to some embodiments, control of thevalve 77 may include an option to vent a portion of the flow to a carbonfilter 86 so as to remove excess analyte or to flush the fluid path 14.In some embodiments, the valve 77 may be configured to provide variableconcentration of the analyte to the instrument 20. For example, if thevalve 77 is a split valve, then the controller 68 may be configured tocontrol the split valve to control a quantity of fluid flowing to theinstrument 20.

According to some embodiments, the flow rate through themicro-concentrator 24 may be less than an optimal or necessary flow rateutilized by the instrument 20. For example, as noted above, the flowrate through the micro-concentrator 24 may be less than 50 mL/min whilethe operable range of fluid flow through some analytical instruments maybe greater than 100 mL/min. As such, a supplemental line 88 with anoptional filter 90 (such as a carbon filter) may provide additionalflow. An additional valve 92 may control the additional flow into thevaporized analyte.

Once the analyte (control) is measured and an instrument responserecorded, it may be determined whether enough data has been acquired fora standard curve (Decision Block 96). The number of control measurementsnecessary or desired for a standard curve varies, generally three ormore control measurements are preferred. In that instance (“Yes” branchof Block 96), the sample (or unknown) may be evaluated using theinstrument 22 (Block 98) and the process may end. Otherwise (“No” branchof Block 96), a next micro-concentrator may be selected (Block 100). Thenext micro-concentrator may be similar to the microcalibrator 10 of FIG.1; however, the next micro-concentrator has a solid sorbent that isconfigured to absorb the analyte at a concentration that is differentfrom the solid sorbent 44 of the previous microcalibrator 10. As notedabove, the amount of analyte absorbed depends on an amount and tailoredcharacter of the solid sorbent composition. The procedure then returnsto loading analyte into the next micro-concentrator.

For example, a calibration curve generally requires at least a lowconcentration of the analyte and a high concentration of the analyte.Thus, according to this particular embodiment, first pre-concentratorwith very little solid sorbent to provide the low concentration sample,and a second pre-concentrator with a large quantity of solid sorbent toprovide the high concentration sample.

In some embodiments, the method may involve closing an isolation valveimmediately after the analyte is directed to the instrument 22.

In some embodiments, the fluid flow passes to a thermal desorption tubeor probe prior to reaching the instrument 22.

In some embodiments, other optional elements may be included. Forexample, the device may include a data port operably connected to thecontroller 68, which enables, for example, the controller 68 to receivefirmware updates or to send information as needed. Alternatively, thecontroller 68 may include devices configured for wireless communication.

In some embodiments, the microcalibrator 10 may include a display or alight. For example, while analyte is loading onto the solid sorbent 44,a “wait” light may illuminate, or a “wait” message may be displayed;then, when the analyte loading has completed, a “ready” light mayilluminate or a “ready” message may be displayed. Additionally oralternatively, the microcalibrator 10 may include a button that signalsto the controller 68 to begin directing the analyte towards theinstrument 20.

According to still other embodiments, and rather than selecting a nextmicrocalibrator as described above, the controller 68 may be used tocontrol one or more of the valves 77, 92 such that a known, controlledflow of the analyte may be combined with a known, controlled flow offluid along the supplemental line 88 such that the ratio of analyte tofluid may be altered. It would be understood by those of ordinaryskilling the art having the benefit of the disclosure made herein thatthe solid sorbent 44 (FIG. 2) of the micro-concentrator 24 should becapable of absorbing a high concentration of analyte. In that way,dilutions of the maximum analyte concentration can be made by the ratioof the analyte to fluid.

While not explicitly illustrated herein, it may be beneficial, such asbetween analytes or after completion of use, to flush themicrocalibrator 10. One manner of doing so, according to one embodiment,may be to open the valves 76, 77, 81 and the pump 78 may be operated,without the introduction of analyte, such that fluid may be directedfrom the fluid source 18 and vented to atmosphere.

Referring now to FIG. 5, a microcalibrator 110 according to anotherembodiment of the present invention is shown and includes a housing 112and a fluid path 114 extending through the housing 112. A first end 116of the fluid path 114 is configured to be operably coupled to the fluidsource 18 (FIG. 1); a second end 118 of the fluid path 114 is configuredto be operably coupled to the instrument 22 (FIG. 1). The fluid path 114may include one or more of a gas trap 120 with its valve 121 and inletline 123, a pump 122, and a valve 124 as was described with reference tothe illustrative embodiment of FIG. 1.

The particular microcalibrator 110 illustrated in FIG. 5 includes a hub126 that is operably and fluidically coupled to the fluid path 114. Thehub 126 may be configured in the manner described previously but, asprovided here, the analyte would flow directly into the fluid path 114as opposed to the micro-concentrator 24 (FIG. 1). Downstream of the hub126, the fluid path 114 may branch such that a first micro-concentrator128, a second micro-concentrator 130, and a third micro-concentrator 132may be arranged in parallel. Corresponding first, second, and thirdvalves 134, 136, 138 may be used to direct flow of analyte from thefluid path 114 to a particular one of the first, second, or thirdmicro-concentrators 128, 130, 132.

The first, second, and third micro-concentrators 128, 130, 132 may beaccording to any of the various embodiments described herein. In fact,the first, second, and third micro-concentrators 128, 130, 132 may havesimilar structures according to a specific embodiment or may havediffering structures according to a plurality of embodiments. Forexample, one or more of the micro-concentrators 128, 130, 132 mayinclude a MEMS-style heater plate 46 (FIG. 1), have solid sorbent grown62 onto the plate 60 (as shown in FIG. 3), no plate (not shown), and soforth. Generally, the first, second, and third micro-concentrators 128,130, 132 may vary by solid sorbent composition therein (not shown inFIG. 5) such that each of the first, second, and thirdmicro-concentrators 128, 130, 132 absorbed a different concentration ofanalyte. In this way, a single microcalibrator 100 may be used forestablishing a three-point calibration curve. However, additionalmicro-concentrators may be included or a plurality of themicrocalibrators 110 may be used for establishing a six-point or anine-point calibration curve, for example.

Downstream of each micro-concentrator 128, 130, 132 there may be acorresponding valve 140, 142, 144 and vent 146, 148, 150 to control aflow of analyte to the instrument 22 (FIG. 1). A supplemental line 152with an optional filter 154 (such as a carbon filter) may provideadditional flow. An additional valve 156 may control the additional flowinto the vaporized analyte. A controller 158 may be included to controlvalves 124, 134, 136, 138, 140, 142, 144, 156, the pump 122, or otheradditional features according to other embodiments of the presentinvention. Thus, signals from the controller 158 may operate the variousvalves 124, 134, 136, 138, 140, 142, 144, 156 and/or the pump 122 toprovide fluid to one or more of the micro-concentrators 128, 130, 132 inorder to direct a known quantity of the analyte to the instrument 22(FIG. 1).

Turning now to FIG. 6, a microcalibrator 160 according to still anotherembodiment of the present invention is shown and includes a housing 162and a fluid path 164 extending through the housing 162. A first end 166of the fluid path 164 is configured to be operably coupled to the fluidsource 18 (FIG. 1); a second end 168 of the fluid path 164 is configuredto be operably coupled to the instrument 22 (FIG. 1). The fluid path 164may include one or more of a gas trap 170 with its valve 171 and inletline 173, a pump 172, and a valve 174 as was described with reference tothe illustrative embodiment of FIG. 1.

For the particular microcalibrator 160 illustrated in FIG. 6, the fluidpath 164 may branch such that a first micro-concentrator 178 and asecond micro-concentrator 180 may be arranged in parallel. Correspondingfirst and second valves 182, 184 may be used to direct flow of analytefrom the fluid path 164 to a particular one of the first and secondmicro-concentrators 178, 180.

Unlike the microcalibrator 110 of FIG. 5, each of the first and secondmicro-concentrators 178, 180 includes a hub 186, 188 in the mannerdescribed in FIGS. 1 and 2. This particular embodiment permits twoanalyte sources (not shown in FIG. 6) to be coupled to the first andsecond micro-concentrators simultaneously.

The first and second micro-concentrators 178, 180 may be according toany of the various embodiments described herein. In fact, the first andsecond micro-concentrators 178, 180 may have similar structuresaccording to a specific embodiment or may have differing structuresaccording to a plurality of embodiments. For example, one or more of themicro-concentrators 178, 180 may include a MEMS-style heater plate 46(FIG. 1), have solid sorbent grown 62 onto the plate 60 (as shown inFIG. 3), no plate (not shown), and so forth. Generally, the first andsecond micro-concentrators 178, 180 may vary by solid sorbentcomposition therein (not shown in FIG. 6) such that each of the firstand second micro-concentrators 178, 180 absorbed a differentconcentration of analyte

Downstream of each micro-concentrator 178, 180 there may be acorresponding valve 190, 192 and vent 194, 196 to control a flow ofanalyte to the instrument 22 (FIG. 1). A supplemental line 198 with anoptional filter 200 (such as a carbon filter) may provide additionalflow. An additional valve 202 may control the additional flow into thevaporized analyte. A controller 204 may be included to control valves174, 182, 184, 190, 192, 202, the pump 172, or other additional featuresaccording to other embodiments of the present invention. Thus, signalsfrom the controller 204 may operate the various valves 174, 182, 184,190, 192, 202 and/or the pump 172 to provide fluid to one or more of themicro-concentrators 178, 180 in order to direct a known quantity of theanalyte to the instrument 22 (FIG. 1).

While in some embodiments of the present invention the device and methodmay be used semi-autonomously for use with a wide variety of fieldequipment. In other embodiments the device and method can be configuredfor autonomous use, where it is either independent of instrumentation,or is attached to an instrument.

The following examples illustrate particular properties and advantagesof some of the embodiments of the present invention. Furthermore, theseare examples of reduction to practice of the present invention andconfirmation that the principles described in the present invention aretherefore valid but should not be construed as in any way limiting thescope of the invention.

EXAMPLE 1

Three microcalibrator according to an embodiment of the presentinvention were used to provide dimethyl methyl phosphonate (“DMMP”), asimulant of sarin (“GB”), standard to a gas chromatograph. Eachmicrocalibrator was configured to provide a distinct, pre-establishedconcentration of standard as described herein.

FIG. 7 is a graphical representation of a calibration curve resultingfrom conventional analyte injection methods.

Using the calibration curve of FIG. 7, replications of 10 ng, 20 nm, and30 nm samples were tested. FIGS. 8, 9, and 10 graphically illustrate theresultant data, respectively, which are also presented in tabularformat, below.

FIG. 11 is a calibration curve resulting from the injection of analytefrom a microcalibrator according to an embodiment of the presentinvention.

10 nm Replicate Area Measure ng Dashed line 5052 8.13 Dotted line 4835.27.83 Solid line 5225.7 8.37 SD 195.7 0.3 Average 5037.9 8.1 % RelativeSD 3.88 3.36

20 nm Replicate Area Measured ng Dashed line 10638 15.92 Dotted line10545 15.79 Solid line 10442 15.64 SD 98.0 0.1 Average 10541.7 15.8 %Relative SD 0.93 0.87

40 nm Replicate Area Measured ng Dashed line 27570 39.52 Dotted line28636 41.01 Solid line 28496 40.82 SD 579.3 0.8 Average 28234.0 40.5 %Relative SD 2.05 2.00

EXAMPLE 2

A microcalibrator according to an embodiment of the present inventionwas used to supply a semi-volatile, methyl salicylate to aphotoionization detector (here, the ppbRae device from RAE Systems Co.,Sunnyvale, Calif.). Data presented in the table, below, demonstrate thereliability of the microcalibrator in providing standards at twoconcentrations (two concentrations were used because the lower level wasbelow the sensitivity of the instrument) to two different detectors:

Micro-Calibrator Concentration Medium High (ng) Avg Peak (ppb) SD AvgPeak (ppb) SD 1625 41.59 3.62 147.82 15.31 1622 30.09 3.40 113.53 9.45

EXAMPLE 3

FIGS. 12 and 13 are calibration curves resulting from the use of aHAPSITE ER in calibrating thermal desorption tubes. FIG. 12 is thecalibration curve resulting from manual injections of 10 ng, 50 ng, and100 ng standards. FIG. 13 is the calibration curve resulting frominjections made using a microcalibrator according to an embodiment ofthe present invention.

EXAMPLE 4

FIG. 14 is a chromatograph of injections of DMMP using a “low”concentration microcalibrator according to an embodiment of the presentinvention. The solid line trace resulted from an injection made while aDMMP analyte source was coupled to the microcalibrator. The dashed linetrace resulted from an injection made after the DMPP analyte source wasreplaced with an empty analyte bottle.

FIG. 15 is also a chromatograph resulting from injections of DMMP usingthe “10 ng” microcalibrator. The solid line trace resulted from thefirst injection after the DMMP analyte source was replaced with an emptyanalyte bottle. The dashed line trace resulted from a 10^(th) injectionfrom the empty analyte bottle. The dotted line trace results from the23^(rd) injection from the empty analyte bottle.

Comparison of the chromatographs within each of FIGS. 14 and 15 suggeststhere may be dosing of the solid sorbent with the analyte and primingthe microcalibrator may be necessary prior to use for calibration. Theanalyte peak does subside, which may suggest the PEEK, TEFLON, or bothmay play a role in dosing.

Use of inert tubing may resist the demonstrated analyte memoryretention.

And so, particularly when a low vapor pressure analyte, heating theanalyte source, one or more fluid lines within the microcalibrator, orboth may be necessary to resolve vapor pressure retention issues.

While the present invention has been illustrated by a description of oneor more embodiments thereof and while these embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus andmethod, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope of the general inventive concept.

What is claimed is:
 1. A method for solventless calibration, the methodcomprising: positioning a microcalibrator in fluid communication with ananalytical instrument, the microcalibrator having a solid sorbenttherein; loading the solid sorbent with an analyte at a firstconcentration; initiating a fluid flow through the microcalibrator suchthat the analyte desorbs from the solid sorbent at the firstconcentration and flows into the analytical instrument; loading thesolid sorbent with the analyte at a second concentration; initiating thefluid flow through the microcalibrator such that the analyte desorbsfrom the solid sorbent at the second concentration to the analyticalinstrument; and generating a calibration curve from measured responsesof the analytical instrument relative to the analyte at the firstconcentration and the analyte at the second concentration.
 2. The methodof claim 1, further comprising: operably coupling an analyte source tothe microcalibrator to load the solid sorbent with analyte.
 3. Themethod of claim 2, further comprising: heating the analyte source. 4.The method of claim 1, wherein a rate of fluid flow ranges from 5 mL/minto 100 mL/min.
 5. The method of claim 1, further comprising: heating thesolid sorbent to further desorb analyte from the solid sorbent.
 6. Themethod of claim 1, further comprising: heating the flowing fluid.
 7. Themethod of claim 1, further comprising: loading the solid sorbent withthe analyte at a third concentration; initiating a fluid flow throughthe microcalibrator such that the analyte desorbs from the solid sorbentat the third concentration and flows into the analytical instrument; andgenerating the calibration curve from measured responses of theanalytical instrument relative to the analyte at the firstconcentration, the analyte at the second concentration, and the analyteat the third concentration.
 8. The method of claim 1, wherein the solidsorbent of the microcalibrator comprises a graphitized carbon black,activated carbon, a porous polymer, or a xerogel.
 9. The method of claim8, wherein the solid sorbent is 2,6-diphenyl-p-phenylene oxide or SiO₂.10. The method of claim 1, further comprising: altering the fluid flowso as to adjust the first concentration, the second concentration orboth to a third concentration.